Systems and methods for arc detection and drag adjustment

ABSTRACT

Controlling a level of electrosurgical energy provided to tissue based on detected arcing patterns or impedance changes. The drag force imposed on an electrode or blade of an electrosurgical instrument may be controlled by adjusting the level of electrosurgical energy based on the arcing patterns or impedance changes. The arcing patterns or impedance changes may be detected by sensing and analyzing voltage and/or current waveforms of the electrosurgical energy. The current and/or voltage waveform analysis may involve calculating impedance based on the voltage and current waveforms and calculating changes in impedance over time. The waveform analysis may involve detecting harmonic distortion using FFTs, DFTs, Goertzel filters, polyphase demodulation techniques, and/or bandpass filters. The waveform analysis may involve determining a normalized difference or the average phase difference between the voltage and current waveforms.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a continuation application of U.S. patentapplication Ser. No. 14/182,797, filed on Feb. 18, 2014, now U.S. Pat.No. 9,498,275 which claims the benefit of and priority to U.S.Provisional Patent Application No. 61/784,141, filed on Mar. 14, 2013,the entire contents of which are incorporated herein by reference.

BACKGROUND

1. Technical Field

The present invention relates generally to electrosurgical systems andmethods and, more particularly, to systems and methods for arc detectionand drag adjustment.

2. Background of Related Art

Electrosurgical instruments have become widely used by surgeons inrecent years. Accordingly, a need has developed for equipment that iseasy to handle and operate, reliable, and safe. Most electrosurgicalinstruments typically include a hand-held instrument that appliesradio-frequency (RF) alternating current to the target tissue. Thealternating current is returned to the electrosurgical source via areturn electrode pad positioned under a patient (i.e., a monopolarsystem configuration) or a return electrode positionable in bodilycontact with or immediately adjacent to the surgical site (i.e., abipolar system configuration). One very common waveform produced by theRF source yields a predetermined electrosurgical effect that results inthe cutting of tissue or the stopping or reducing of bleeding.

In particular, electrosurgical fulguration comprises the application ofan electric spark to biological tissue, for example, human flesh or thetissue of internal organs, with minimal cutting. Generally, fulgurationis used to dehydrate, shrink, necrose, or char the tissue. As a result,this technique is primarily used to stop bleeding and oozing. Theseoperations are generically embraced by the term “Coagulation.”Meanwhile, electrosurgical cutting includes the use of the appliedelectric spark to cut tissue. Electrosurgical sealing includes utilizingboth pressure and electrosurgically generated heat to melt the tissuecollagen into a fused mass that prevents bleeding from the fused tissue.

As used herein the term “electrosurgical pencil” is intended to includemonopolar electrosurgical instruments which have a handpiece which isattached to an active electrode and are used to coagulate, cut, and/orseal tissue. The electrosurgical pencil may be operated by a handswitchor a foot switch. The active electrode is an electrically conductingelement which is usually elongated and may be in the form of a thin flatblade with a pointed or rounded distal end. Alternatively, the activeelectrode may include an elongated narrow cylindrical needle which issolid or hollow with a flat, rounded, pointed, or slanted distal end.Typically, electrodes of this sort are known in the art as “blade,”“loop” or “snare,” or “needle” or “ball” electrodes.

The handpiece of the electrosurgical instrument is connected to asuitable electrosurgical source, such as an electrosurgical generator,which produces radio-frequency alternating current necessary for theoperation of the electrosurgical instrument. In general, when anoperation is performed on a patient with an electrosurgical instrument,alternating current from the electrosurgical generator is conductedthrough the active electrode to the tissue at the site of the operation(the target tissue) and then through the patient to a return electrode.The return electrode is typically placed at a convenient place on thepatient's body and is attached to the generator by a conductivematerial.

During a surgical procedure, an operator moves the electrode or blade ofthe electrosurgical instrument through the tissue at a desired speeddepending on, among other things, the skill of the operator and the typeof tissue that is being treated. Oftentimes, however, the speed at whichthe operator can move the electrode of the electrosurgical instrumentthrough the tissue is limited by a force that opposes the movement ofthe electrosurgical instrument through the tissue. This force isreferred to as drag. The drag not only limits the operator's ability tomore quickly and efficiently complete a surgical procedure, but alsolimits the operator's ability to easily adapt during the surgicalprocedure to different tissue types and characteristics, which maypresent different drag profiles.

SUMMARY

The present disclosure relates to electrosurgical systems and methodsthat provide an operator with the ability to set the drag or dragprofile exhibited by the cutting tip of an electrosurgical instrument,as the cutting tip is advanced through tissue.

In aspects, the present disclosure features a method of controllingelectrosurgical energy provided by an electrode of an electrosurgicalinstrument to tissue. The method includes delivering electrosurgicalenergy to the electrode of the electrosurgical instrument, sensingarcing patterns between the electrode and tissue, and controlling thelevel of electrosurgical energy delivered to the electrode based on thesensed arcing patterns.

The method of controlling electrosurgical energy may include determiningdrag based on the sensed arcing patterns, and controlling the level ofelectrosurgical energy delivered to the electrode based on thedetermined drag and a predetermined drag value. Controlling the level ofenergy delivered to the electrode may include increasing the power ofthe electrosurgical energy delivered to the electrode if the determineddrag is greater than the predetermined drag value and decreasing thepower of the electrosurgical energy delivered to the electrode if thedetermined drag is less than the predetermined drag value. Controllingthe level of energy delivered to the electrode may include adjusting theduty cycle of the RF waveform to change the drag. The method ofcontrolling electrosurgical energy may include receiving thepredetermined drag value from a user interface, or reading thepredetermined drag value from a bar code, an RFID tag, or a memoryassociated with the electrosurgical instrument.

The arcing patterns may be sensed by sensing at least one of the voltageand current waveforms of the electrosurgical energy delivered to theelectrode, and detecting harmonic distortion of the at least one of thevoltage and current waveforms. The harmonic distortion may be detectedby filtering with respect to frequency at least one of the voltage andcurrent waveforms. For example, the harmonic distortion may be detectedby applying a Fast Fourier Transform (FFT), a Discrete Fourier Transform(DFT), a Goertzel filter, or a narrow-band filter to at least one of thevoltage and current waveforms. Detecting harmonic distortion may involvedetecting at least one of the second, third, and fifth harmonics of atleast one of the voltage and current waveforms.

The arcing patterns may be sensed by sensing the voltage and currentwaveforms of the electrosurgical energy delivered to the electrode, andcalculating the normalized difference between the voltage and currentwaveforms.

The arcing patterns may be sensed by sensing the voltage and current ofthe electrosurgical energy, calculating the phase difference between thevoltage and current of the electrosurgical energy, calculating theaverage phase difference over a predetermined time interval, and sensingthe arcing patterns based on the average phase difference.

The arcing patterns may be sensed by sensing the voltage and current ofthe electrosurgical energy, calculating impedance based on the sensedvoltage and current, and detecting the arcing patterns based on thechange in calculated impedance over time. For example, sensing arcsstarting and stopping over time scales of 1 ms may indicate rapidchanges in impedance.

The arcing patterns may be sensed by sensing impedance between theelectrode and tissue, detecting arcing if a low inductive impedance issensed, detecting a loss of arcing if a high capacitive impedance issensed, and detecting contact with tissue if a resistive impedance issensed.

The method of controlling electrosurgical energy provided by anelectrode of an electrosurgical instrument to tissue may includedetermining drag based on the sensed impedance, and controlling thelevel of electrosurgical energy delivered to the electrode based on thedetermined drag and a predetermined drag value. Determining drag mayinclude determining a low level of drag if a high capacitive impedanceis sensed, and determining a high level of drag if a primarily resistiveimpedance is sensed.

Controlling the level of energy delivered to the electrode may includeincreasing the power of the electrosurgical energy delivered to theelectrode if the determined drag force is greater than the predetermineddrag force setting and decreasing the power of the electrosurgicalenergy delivered to the electrode if the determined drag force is lessthan the predetermined drag force setting.

In further aspects, the present disclosure features an electrosurgicalgenerator for providing electrosurgical energy to an electrode of anelectrosurgical instrument. The electrosurgical generator includes anoutput stage that provides electrosurgical energy to the electrode ofthe electrosurgical instrument, a sensor that senses arcing patterns ofthe electrosurgical energy provided to the tissue by the electrode, anda controller coupled to the output stage and the sensor. The controllercontrols the level of electrosurgical energy delivered to the electrodebased on the sensed arcing patterns.

The controller may determine a drag force on the electrode of theelectrosurgical instrument based on the sensed arcing patterns andcontrol the level of electrosurgical energy delivered to the electrodebased on the determined drag force and a drag force setting. Theelectrosurgical generator may include a user interface that provides thedrag force setting to the controller in response to a user selection.

The sensor may include at least one of a voltage sensor and a currentsensor, and the controller may detect harmonic distortion of at leastone of the voltage and current waveforms output from at least one of thevoltage and current sensors, respectively. The controller detectsharmonic distortion of at least one of the voltage and current waveformsby filtering with respect to the frequency of at least one of thevoltage and current waveforms. For example, the controller may detectharmonic distortion of at least one of the voltage and current waveformsby applying a Goertzel filter, a narrow-band filter, or a Fast FourierTransform (FFT) to at least one of the voltage and current waveforms.The controller may detect arcing patterns by sensing at least one of thesecond, third, and fifth harmonics of at least one of the voltage andcurrent waveforms.

The sensor may include a voltage sensor and a current sensor that sensethe voltage and current waveforms of the electrosurgical energy, and thecontroller may calculate a normalized difference between the voltage andcurrent waveforms to sense arcing patterns.

The sensor may include a voltage sensor and a current sensor that sensethe voltage and current waveforms of the electrosurgical energy, and thecontroller may calculate impedance based on the sensed voltage andcurrent waveforms, and determine arcing patterns based on the change incalculated impedance over time.

The sensor may sense impedance between the electrode and tissue, and thecontroller may detect arcing if a low inductive impedance is sensed,detect a loss of arcing when a high capacitive impedance is sensed, anddetect contact with tissue if a resistive impedance is sensed.

The sensor may include a voltage sensor that senses a voltage waveformof the electrosurgical energy and a current sensor that senses a currentwaveform of the electrosurgical energy, and the controller may calculatea phase difference between the voltage and current waveforms, calculatean average phase difference between the voltage and current waveformsover a predetermined time interval, and determine arcing patterns basedon the average phase difference.

The controller may determine drag based on a sensed arcing pattern orthe sensed impedance, and control the level of electrosurgical energydelivered to the electrode based on the determined drag and apredetermined drag value. The controller may calculate a phasedifference between the voltage and current waveforms, calculate anaverage phase difference between the voltage and current waveforms overa predetermined time interval, and determine arcing patterns based onthe average phase difference.

The controller may control the level of electrosurgical energy deliveredto the electrode by increasing the power delivered to the electrode ifthe determined drag is greater than the predetermined drag value and bydecreasing the power of the electrosurgical energy delivered to theelectrode if the determined drag is less than the predetermined dragvalue.

In still further aspects, the present disclosure features anelectrosurgical system including an electrosurgical instrument thatdelivers electrosurgical energy to tissue and an electrosurgicalgenerator coupled to the electrosurgical instrument. The electrosurgicalgenerator includes an output stage that generates the electrosurgicalenergy, a sensor that senses arcing patterns of the electrosurgicalenergy provided to the tissue by the electrode of the electrosurgicalinstrument, and a controller coupled to the output stage and the sensor.The controller controls the level of electrosurgical energy delivered tothe electrode based on the sensed arcing patterns.

These and other objects will be more clearly illustrated below by thedescription of the drawings and the detailed description of thepreferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate embodiments of the invention and,together with a general description of the invention given above, andthe detailed description of the embodiments given below, serve toexplain the principles of the invention.

FIG. 1 is a perspective view of an electrosurgical system including anelectrosurgical generator, an electrosurgical instrument, and a returnpad, according to embodiments of the present disclosure;

FIG. 2 is a front view of the electrosurgical generator of FIG. 1;

FIG. 3 is a schematic block diagram of the electrosurgical generator ofFIG. 1;

FIG. 4 is a diagram illustrating arcing during an electrosurgicalprocedure using the electrosurgical instrument of FIG. 1;

FIG. 5A is a graphical diagram illustrating the relationships among dragforce, speed, and electrosurgical power for the electrosurgicalprocedure illustrated in FIG. 4;

FIG. 5B shows graphical diagrams illustrating the relationships amongspeed, drag force, and phase between the voltage and current of theelectrosurgical energy delivered to the tissue for the surgicalprocedure illustrated in FIG. 4;

FIG. 6 is a graphical diagram of the voltage and current of an arcingpattern during an electrosurgical cutting procedure;

FIG. 7 is a flow diagram of a method of controlling electrosurgicalenergy delivered to an electrode of an electrosurgical instrument basedon sensed arcing patterns according to embodiments of the presentdisclosure.

FIG. 8 is a flow diagram of a method of controlling electrosurgicalenergy to achieve a user-selected drag force based on sensed arcingpatterns according to embodiments of the present disclosure;

FIG. 9 is a flow diagram of a method of detecting arcing patterns basedon impedance according to embodiments of the present disclosure;

FIG. 10 is a flow diagram of a method of detecting arcing patterns basedon the harmonic distortion of at least one of sensed voltage and currentwaveforms and controlling the cutting speed of drag on anelectrosurgical instrument according to embodiments of the presentdisclosure;

FIG. 11 is a flow diagram of a method of detecting arcing patterns basedon impedance and controlling drag based on the detected arcing patternsaccording to embodiments of the present disclosure; and

FIG. 12 is a flow diagram of a method of sensing arcing patterns basedon the average phase difference according to embodiments of the presentdisclosure.

DETAILED DESCRIPTION

Embodiments of the present disclosure are described in detail withreference to the drawing figures wherein like reference numeralsidentify similar or identical elements. As used herein, the term“distal” refers to the portion that is being described which is fartherfrom a user, while the term “proximal” refers to the portion that isbeing described which is closer to a user.

The systems and methods of the present disclosure allow an operator tocontrol the drag force imposed on a monopolar electrosurgical instrumentdepending on, among other things, the skill of the operator and thedifferent types and characteristics of tissue that are encountered bythe operator during a surgical procedure. The present disclosure isdirected to systems and methods for detecting arcing patterns orimpedance changes and adjusting the power of the electrosurgicalgenerator so that the drag force imposed on the blade of anelectrosurgical instrument can be controlled to a user-selected dragforce level based on the detected arcing patterns or impedance changes.The arcing or impedance patterns may be detected by sensing voltageand/or current waveforms used to cut tissue and analyzing the sensedvoltage and/or current waveforms. The current and/or voltage waveformanalysis may involve calculating impedance or complex impedance anddetermining patterns in the calculated impedance.

Alternatively, the waveform analysis may involve detecting harmonicdistortion using FFTs, DFTs, Goertzel filters, polyphase demodulationtechniques, and/or narrow-band filters. The harmonic distortion may bedetected by monitoring one or more frequency components of the voltageand current waveforms, such as the second, third, and/or fifth harmonicsof the voltage and current waveforms. The frequency components may alsoinclude side bands associated with the harmonics of the fundamental RFfrequency.

Time domain techniques may also be employed to detect arcing patterns.In some embodiments, the difference between the voltage and currentwaveforms, e.g., the normalized difference between the voltage andcurrent waveforms, may be calculated to detect arcing patterns. In otherembodiments, arcing patterns may be detected by sensing compleximpedance patterns. A low inductive impedance may indicate arcing, ahigh capacitive impedance may indicate that there is no arcing, and aresistive tissue impedance may indicate direct contact with tissue.

A generator according to the present disclosure can perform monopolarand/or bipolar electrosurgical procedures, including vessel sealingprocedures. The generator may include a plurality of outputs forinterfacing with various electrosurgical instruments (e.g., a monopolarinstrument, return electrode, bipolar electrosurgical forceps,footswitch, etc.). Further, the generator includes electronic circuitryconfigured to generate radio frequency energy specifically suited forvarious electrosurgical modes (e.g., cutting, blending, division, etc.)and procedures (e.g., monopolar, bipolar, vessel sealing). Inembodiments, the generator may be embedded, integrated, or otherwisecoupled to the electrosurgical instruments providing for an all-in-oneelectrosurgical apparatus.

FIG. 1 is a schematic illustration of an electro surgical system 100according to the present disclosure. The system 100 may include one ormore monopolar electrosurgical instruments 2 having one or moreelectrodes (e.g., electrosurgical cutting probe, ablation electrodes,etc.) for treating tissue of a patient. Electrosurgical alternatingcurrent is supplied to the instrument 2 by a generator 200 via a supplyline 4 that is connected to an active terminal 330 (FIG. 3) of thegenerator 200, allowing the instrument 2 to coagulate, ablate, cut,and/or otherwise treat tissue. The alternating current is returned tothe generator 200 through a return electrode 6 via a return line 8 at areturn terminal 332 (FIG. 3) of the generator 200. The system 100 mayinclude a plurality of return electrodes 6 that are disposed on apatient to minimize the chances of tissue damage by maximizing theoverall contact area with the patient. In addition, the generator 200and the return electrode 6 may be configured to monitor contact betweenthe return electrodes 6 and tissue to ensure that sufficient contactexists between them to further minimize chances of unintended tissuedamage.

With reference to FIG. 2, a front face 240 of the generator 200 isshown. The generator 200 may be any suitable type (e.g.,electrosurgical, microwave, etc.) and may include a plurality ofconnectors 250-262 to accommodate various types of electrosurgicalinstruments (e.g., electrosurgical forceps 10). The connectors 250-262may include various detection devices that can read (e.g., scan, decode,etc.) identifying information encoded or otherwise recorded on or withinthe plugs or cables of the instruments. The connectors 250-262 areconfigured to decode the information encoded on the plugs correspondingto the operating parameters of particular instruments allowing thegenerator 200 to preset energy delivery settings or drag settings basedon the connected instrument. In embodiments, data may be encoded in barcodes, electrical components (e.g., resistors, capacitors, etc.), RFIDchips, magnets, non-transitory storage (e.g., non-volatile memory,EEPROM, etc.), which may then be coupled to or integrated into the plug.Corresponding detection devices may include, but are not limited to, barcode readers, electrical sensors, RFID readers, Hall Effect sensors,memory readers, etc., and any other suitable decoders configured todecode data.

The generator 200 includes one or more display screens 242, 244, 246 forproviding the user with a variety of output information (e.g., intensitysettings, treatment complete indicators, etc.). Each of the screens 242,244, 246 is associated with corresponding connectors 250-262. Thegenerator 200 includes suitable input controls (e.g., buttons,activators, switches, touch screen, etc.) for controlling the generator200. The display screens 242, 244, 246 may be configured as touchscreens that display a corresponding menu for the electrosurgicalinstruments (e.g., electrosurgical forceps, etc.). The user can thenmakes inputs by simply touching corresponding menu options.

Screen 242 controls monopolar output and the devices connected to theconnectors 250 and 252. The screen 242 includes a portion 232 thatallows an operator to set a desired drag force for the monopolar deviceconnected to connector 250. Specifically, the screen 242 includesbuttons 236 and 238, which allow an operator to increase or decrease thedrag force setting. The screen 242 also displays the current drag forcesetting 234, which, as shown in FIG. 2, is 0.3. The connector 250 isconfigured to couple to a monopolar electrosurgical instrument (e.g., anelectrosurgical pencil) and connector 252 is configured to couple to afoot switch (not shown). The foot switch provides for additional inputs,which may replicate inputs of the generator 200. Screen 244 controlsmonopolar and bipolar output and the devices connected to connectors 256and 258. Connector 256 is configured to couple to other monopolarinstruments. Connector 258 is configured to couple to a bipolarinstrument (not shown). Screen 246 controls vessel sealers connected toconnectors 260 and 262.

FIG. 3 shows a schematic block diagram of the generator circuitry 300 ofthe generator 200 of FIGS. 1 and 2, which is configured to outputelectrosurgical energy. The generator circuitry 300 includes a userinterface 305, a controller 324, a power supply 327, and an output stage328. The power supply 327 may be a direct current high voltage powersupply and may be connected to an AC source (e.g., line voltage). Thepower supply 327 provides high voltage DC power to an output stage 328,which then converts high voltage DC power into electrosurgicalalternating current and provides the electrosurgical energy to theactive terminal 330. The alternating current is returned to the outputstage 328 via the return terminal 332. The output stage 328 isconfigured to operate in a plurality of modes, during which thegenerator circuitry 300 outputs corresponding waveforms having specificduty cycles, peak voltages, crest factors, etc. In other embodiments,the generator circuitry 300 may be based on other types of suitablepower supply topologies.

The controller 324 includes a processor 325 (e.g., a microprocessor)operably connected to a memory 326, which may include transitory typememory (e.g., RAM) and/or non-transitory type memory (e.g., flash mediaand disk media). In embodiments, the controller 324 may further includea field-programmable gate array (FPGA) for performing real-time analysisof the delivered current and/or voltage waveforms, as described below.The processor 325 includes an output port that is operably connected tothe power supply 327 and/or output stage 328 allowing the processor 325to control the output of the generator circuitry 300 according to eitheropen- and/or closed-loop control schemes. Those skilled in the art willappreciate that the processor 325 may be substituted by any logicprocessor (e.g., control circuit) adapted to perform the calculationsand/or set of instructions discussed herein.

The generator circuitry 300 implements a closed-loop feedback controlsystem, in which a plurality of sensors measure a variety of tissue andgenerator output properties (e.g., tissue impedance, tissue temperature,output power, current and/or voltage, etc.), and provide feedback to thecontroller 324. The controller 324 then signals the power supply 327and/or output stage 328, which then adjusts the DC power supply and/oroutput stage, respectively. The controller 324 also receives inputsignals from the user interface 305 of the generator circuitry 300. Thecontroller 324 utilizes input signals received through the userinterface 305 to adjust power outputted by the generator circuitry 300and/or performs other control functions thereon. According to thepresent disclosure, an operator may input a desired drag setting via theuser interface 305. For example, some surgeons prefer high drag toreduce the probably of accidentally cutting into undesired areas. Thus,these surgeons may input a desired drag setting via the user interface305 that provides a high drag level. In general, this would slow therate of cutting.

In embodiments, the desired drag setting or a default drag setting maybe programmed into memory disposed within the instrument 2 or stored ina bar code or radio-frequency identification (RFID) tag disposed on theinstrument 2. The desired drag setting may also be deduced from thesurgeon's rate of cutting. For example, the controller 324 may determinethe average drag experienced by the surgeon based on arc patterns, setthe desired drag setting to the average drag, and adjust the outputpower or voltage to achieve the desired drag setting. The controller 324may perform these functions during an auto-drag mode, which may be setby the surgeon.

The controller 324 retrieves and uses the desired drag setting to adjustthe power of the electrosurgical output from the output stage 328 basedon sensed arcing patterns and/or the impedance patterns between theelectrosurgical instrument 2 and the tissue.

The generator circuitry 300 according to the present disclosure includesan RF current sensor 380 and an RF voltage sensor 370. The RF currentsensor 380 is coupled to the active terminal 330 and providesmeasurements of the RF current supplied by the output stage 328. The RFvoltage sensor 370 is coupled to the active and return terminals 330 and332, and provides measurements of the RF voltage supplied by the outputstage 328. In embodiments, the RF voltage and current sensors 370 and380 may be coupled to active lead 331 and return lead 333, whichinterconnect the active and return terminals 330 and 332 to the outputstage 328, respectively.

The RF voltage and current sensors 370 and 380 provide the sensed RFvoltage and current signals, respectively, to analog-to-digitalconverters (ADCs) 302. The ADCs 302 sample the sensed RF voltage andcurrent signals and provide digital samples of the sensed RF voltage andcurrent signals to the controller 324, which then may adjust the outputof the power supply 327 and/or the output stage 328 in response to thedigital samples of the sensed RF voltage and current signals. Variouscomponents of the generator circuitry 300, namely, the output stage 328and the RF voltage and current sensors 370 and 380, may be disposed on aprinted circuit board (PCB).

FIG. 4 is a diagram illustrating arcing during a monopolar cuttingprocedure performed by the electrosurgical instrument 2. A surgeon setsthe electrosurgical instrument 2 to a desired drag value via the userinterface 305 of the generator circuitry 300 and activates theelectrosurgical instrument 2 by depressing the activation switch 401,thus permitting alternating current to be transmitted to the cutting tipor blade 405. The surgeon then commences the electrosurgical procedureby touching the cutting tip or blade 405 to the target tissue 420.

There is evidence that the process of monopolar cutting precedes theblade 405 of the instrument 2 by arcing 415 to the fresh tissue 425ahead of the blade 405, thus vaporizing the fresh tissue 425 before theblade 405 makes contact with other fresh tissue 425. In other words,arcs 415 form as the blade gets close to the boundary edge of the tissue425 and extinguish once the tissue 425 is vaporized and the boundaryedge moves farther from the blade so that the arcs 415 are extinguished.If the blade is moving slower than the maximum rate of tissue removal,this results in a pattern of arcing, followed by a capacitive state (an“open circuit”) as the arcing extinguishes when all tissue within rangehas been removed. If the blade is moving faster than the maximum rate oftissue removal, a resistive state is achieved as the blade 405 comesinto contact with fresh tissue 425.

If the movement rate of the blade 405 in the direction 410 is slowcompared to the power or voltage setting of the generator 200, then thearc 415 vaporizes the tissue 420 and extinguishes before the blade 405moves close enough to the fresh tissue 425 to reestablish an arc 415.The repeated process of moving the blade 405, creating an arc 415, andextinguishing the arc 415 creates a detectable arc pulse pattern. Thisrepeated process may be detected as a change from an arc 415 to acapacitive impedance.

If, on the other hand, the movement rate of the blade 405 is fastcompared to the power or voltage setting of the generator 200, thenarcing may be reduced because of the constant contact between the blade405 and the tissue 425 or arcing may be at a constant level. Contactbetween the blade 405 and the tissue 425 increases the drag of thetissue on the blade 405. According to embodiments of the presentdisclosure, these arcing patterns are detected and used to determine thedrag of the tissue on the blade 405. The power level of the alternatingcurrent applied to the tissue is then adjusted to achieve a desired dragvalue.

It is contemplated that electrosurgical instrument 2 may be providedwith an audible or visible (i.e., light) feedback system (not shown)which would signal to the operator when the drag acting on the cuttingtip or blade 405 is near, is equal to, or has surpassed a predetermineddrag level. For example, generator 200 and/or the electrosurgicalinstrument 2 may include a buzzer and/or light which are set to beactivated when the sensed drag reaches a certain predetermined dragvalue or falls within a range of drag values. In this manner, theoperator can focus on the target tissue site and be alerted, forexample, by the sound of a buzzer, by the flashing of a light, or byboth, when the resistance acting against the advancement of the cuttingtip 405 has become greater than the predetermined drag value.

FIG. 5A is a graphical diagram 500 illustrating the relationship amongdrag force, speed, and electrosurgical power for the electrosurgicalinstrument 2 during a cutting procedure. The graphical diagram 500includes a first axis 510 indicating the drag force of the tissue on theblade 405 and a second axis 520 indicating the speed or movement rate ofthe blade 405 as it cuts tissue. The graphical diagram 500 shows dragprofile curves 531-534, each of which represents the relationshipbetween drag force and speed at a constant power level, arranged inorder of increasing power levels.

Each of the drag profile curves 531-534 show that the drag forceincreases significantly as the speed of the electrosurgical instrument 2is increased for a given constant power level. In other words, when thesurgeon cuts tissue with the electrosurgical pencil at low and moderatespeeds, there is little resistance to the movement of theelectrosurgical pencil through the tissue. As the speed of cuttingincreases, the resistance remains relatively low until a point at whichthe drag force increases sharply as shown by the drag profile curves531-534.

The drag force increases sharply at the end of the drag profile curvesbecause the arc front does not fully vaporize the tissue 425 before theblade 405 moves into contact with the tissue 425. As shown in FIG. 5A,increasing the power allows for a higher speed with minimal drag becauseincreasing the power increases the tissue vaporization ahead of theblade. For example, if the surgeon makes a shallow cut, then a smallamount of power is needed to vaporize the small amount of tissue, thusreducing drag for a given power level. If the surgeon increases thedepth of the cut, then more power is needed to vaporize the largeramount of tissue to maintain the same drag level.

According to the present disclosure, the drag or the cutting speed ofthe electrosurgical instrument is controlled based on the arcingpatterns or characteristics of the arcs formed between the electrode orcutting tip of the electrosurgical instrument and the tissue and/orbased on the impedance sensed between the electrode and tissue. Thearcing pattern may be a pulse pattern of arcing and loss of arcing. Theloss of arcing may occur when there is an “open circuit” or a relativelyhigh capacitive impedance between the cutting tip of the electrosurgicalinstrument 2 and tissue 425 (e.g., when the blade is moved relativelyslowly) or when there is a resistive impedance between the cutting tipof electrosurgical instrument 2 and tissue when the electrosurgicalinstrument is moved rapidly and comes into contact with tissue.

Thus, the high capacitive impedance between the blade 405 and the tissue425 indicates low drag because the cutting tip of the electrosurgicalinstrument 2 is too far from the tissue to create an arc and the powerof the electrosurgical energy is at a high level. A resistive impedancebetween the blade 405 and the tissue 425 indicates high drag because thecutting tip of the electrosurgical instrument 2 is in contact with thetissue 425 and the power of the electrosurgical energy is at a lowlevel.

In some embodiments, the arcing patterns may include three states ormodes: (1) loss of arcing to tissue, (2) arcing to tissue, and (3)contact with tissue. In other embodiments, the arcing patterns includethe shape or other characteristic of the voltage and/or current waveformof the electrosurgical energy delivered to the tissue. For example, theshape or other characteristic of the harmonic distortion during arcingmay be useful to predict when the cutting tip may come in contact withtissue. The arcing patterns may be macro arcing patterns in the RFwaveform at the 100 μs to 1 ms scale and/or micro arcing pattern in theRF waveform at the 2 to 10 μs scale.

A variety of techniques may be employed to detect the arcing patterns.When an arc forms between the electrode of the electrosurgicalinstrument and tissue, the voltage and/or current waveforms of theelectrosurgical energy that flows to the tissue may change considerably.The techniques for detecting arcing patterns involve detecting thesechanges in the voltage and/or current waveforms.

FIG. 5B shows graphical diagrams 540 and 545 illustrating therelationships among speed, drag force, and the phase between the voltageand current of the electrosurgical energy delivered to tissue for thesurgical procedure illustrated in FIG. 4. Similar to FIG. 5A, graphicaldiagram 540 shows the drag force as a function of a velocity ramp (i.e.,constant acceleration) when constant electrosurgical power is applied totissue having constant thickness. As shown, when the speed reaches aparticular value, the drag force 541 increases sharply. Graphicaldiagram 545 shows the phase difference between the voltage and currentof the electrosurgical power (i.e., axis 550) applied to the tissue as afunction of speed (i.e., axis 520) under the same conditions describedabove with respect to graphical diagram 540. As shown, the phasedifference 546 decreases linearly (i.e., the ramp 548) and then becomesconstant 549 at about the same speed at which the drag force 541 beginsto increase.

The ramp 548 in the phase difference 546 may be caused by the transitionfrom not cutting to cutting at a maximum speed. Thus, theelectrosurgical power may be controlled by monitoring the phasedifference between the voltage and current of the electrosurgical powerand adjusting the output electrosurgical power to maintain a desiredphase difference and thus a desired cutting effect. In some embodiments,if a desired cutting effect occurs at higher speed versus power ratios,the electrosurgical power may be modulated or pulsed to lower the speedversus power ratio for a sufficient amount of time to determine thephase difference and thus the location on the graphical diagram 545.This information may then be used to maintain a particular cuttingeffect by adjusting the output electrosurgical power.

FIG. 6 is a graphical diagram 600 illustrating one technique fordetecting arcing patterns between the electrosurgical instrument 2 andtissue during a surgical procedure. The graphical diagram 600 includes afirst axis 610 indicating the voltage of the electrosurgical energy asmeasured by the voltage sensor 370 of FIG. 3, a second axis 620indicating the current as measured by the current sensor 380 of FIG. 3,and a third axis 630 indicating the time. The voltage waveform 611 andthe current waveform 621 were measured by the voltage sensor 370 and thecurrent sensor 380, respectively, during arcing. The arcing is shown bythe difference between the voltage waveform 611 and the current waveform621. The shape of the current waveform 621 shows the current flow duringthe arc and, when the voltage waveform 611 drops, the arc isextinguished, and then re-established. The current waveform 621 showsdistinct harmonic distortion while the voltage waveform 611 shows littledistortion.

Thus, the controller 324 may be configured to detect arcing when thecontroller 324 detects harmonic distortion or a particular shape orother characteristic of the harmonic distortion in the current waveform621. Alternatively, the controller 324 may be configured to detectarcing when the controller 324 detects harmonic distortion or aparticular shape or other characteristic of the harmonic distortion inthe voltage waveform 611. The amount of harmonic distortion in thevoltage and current waveforms depends on the Thevenin output impedancecompared to the load resistance of the arc events. If the outputimpedance were small compared to the load, then the voltage would berelatively harmonic free, while the current would be distorted. If, onthe other hand, the output impedance were large compared to the loadimpedance, then the current would be relatively harmonic free, while thevoltage would be distorted (e.g., the voltage would droop as the currentrises).

The harmonic distortion of the voltage and current waveforms may bedetected using FFT or DFT frequency decomposition techniques (e.g.,using multiple single frequency DFT algorithms), Goertzel filters, orone or more bandpass filters, demodulation filters, which may beimplemented in the controller 324. For example, the one or more singlefrequency DFT algorithms or the one or more narrowband bandpass filtersmay be configured for one or more harmonic frequencies that areassociated with particular arcing patterns or characteristics, whichindicate the level of drag of the tissue on the blade 405. These filtersmay monitor the second, third, and/or fifth harmonics of the voltage andcurrent waveforms of the electrosurgical energy. In some embodiments,particular harmonics may be detected using polyphase demodulationtechniques, which use a type of decimating digital filter. A polyphasedemodulation technique could be used to create series bandpass filters.According to the polyphase demodulation technique, the frequency orfrequencies of interest are demodulated to baseband (DC frequency) andthe amplitude is sensed at the frequency or frequencies of interest.

Time domain techniques may be used to detect arcing patterns. Forexample, the controller 324 may determine the normalized differencebetween the voltage and current waveforms of the electrosurgical energy.If the normalized difference exceeds a predetermined value, then arcingis detected. Otherwise, arcing is not detected. In embodiments, thecontroller 324 may incorporate an FPGA that performs real-time analysisof the voltage and current waveforms to enable real-time control of thepower and/or waveform of the electrosurgical energy delivered to thetissue.

The arcing patterns may be detected based on the impedance calculatedfrom the voltage sensed by the voltage sensor 370 and the current sensedby the current sensor 380. The arcing or impedance pattern would includea low impedance during an arc and a high impedance when the arcextinguishes.

The arcing patterns described above may be detected based on impedancecalculated using sensed voltage and current waveforms and the phaseshift between them. The impedance would include a low inductiveimpedance during arcing, a high capacitive impedance when not arcing,and a primarily resistive impedance during contact with tissue.

The arcing patterns described above may be detected based on measurementof the time-averaged phase shift between the voltage and currentwaveforms at the electrode. The average phase shift increasesmonotonically from a small value when the electrode is in resistivecontact with the tissue, to progressively higher values as arcing occursfor a larger fraction of the measured time, to even higher values assteady arcing is gradually replaced with the capacitive coupling as theelectrode-tissue separation or gap becomes large enough to extinguishthe arcing.

In yet other embodiments, the arcing pattern described above may bedetected by analyzing the phase characteristics of the voltage andcurrent waveforms. For example, changes in phase between the voltage andcurrent waveforms may indicate transitions between states of the arcingpattern. When voltage is applied to the electrode of the electrosurgicalinstrument and there is no arcing between the electrode and tissue, thevoltage and current waveforms are substantially out of phase because theelectrode and tissue appear like a capacitor. When an arc forms betweenthe electrode and tissue, and when the electrode is passing at a veryslow speed through the tissue, the average phase between the voltage andcurrent waveforms continues to appear capacitive. As the speed of theelectrode through the tissue increases, with the supplied power heldconstant, the average phase between the voltage and current waveformsdecreases in an approximately linear relationship to the speed.

When the electrode speed exceeds the maximum cutting rate at thesupplied power, the electrode remains in contact with the tissue and thephase difference between the voltage and current waveforms isapproximately zero corresponding to a purely resistive circuit. Even ifthe contact between the electrode and the tissue is purely resistive,the measured phase will often include an inductive component due to thewires leading to the electrode and from the patient. This can lead tothe measured phase between the voltage and current waveforms passingthrough zero and becoming somewhat negative.

The changes in phase between the voltage and current may be detected bythe controller 324 using some of the techniques described above. Forexample, the controller 324 may include a zero-crossing detector inwhich the time between zero crossings of the current waveform issubtracted from the time of the zero crossing of the voltage waveform toobtain a time delay. Then, the time delay is converted to a phase shiftbased on the RF frequency. The phase shift between the voltage andcurrent waveforms may also be detected by using a FFT, DFT, or Goertzel,by detecting the phase of each waveform at the specified frequency andthen subtracting the voltage phase result from the current phase result.The phase may also be determined by feeding the sensed voltage andcurrent waveforms to appropriate logic gates (e.g., AND gates),correlating the output from the logic gates, and averaging thecorrelated output from the logic gates. These computations may beperformed in an FPGA of the controller 324.

In some embodiments, the controller 324 may maintain a given powersetting and change the peak voltage or crest factor of theelectrosurgical energy to achieve a desired drag force. In otherembodiments, when the generated electrosurgical energy has a continuouswaveform (e.g., in the cut mode), the RMS voltage may be adjusted toachieve a desired drag force. In yet other embodiments, the controller324 may control the shape of the waveform of the electrosurgical energygenerated by the output stage 328 based on the detected arcing orimpedance patterns to achieve a desired drag force.

The controller 324 may control the drag force or cutting speed bycontrolling the output stage 328 to generate waveform shapes or othercharacteristics of the electrosurgical energy to achieve a desired dragforce or cutting speed. For example, if the surgeon sets a maximumcutting speed (or sets a minimum drag force) having minimal coagulation,the controller 324 may generate cutting waveforms having a 100% dutycycle. If the surgeon decreases the cutting speed (or increases the dragforce), then the controller 324 may generate a cutting waveform having aduty cycle less than 100% (e.g., 50% for blend mode, 25% for V-mode,which modulates the voltage of the coagulation waveform, and 4.7% forfulguration mode). The cutting waveform having a duty cycle less than100% increases the crest factor, which provides more coagulation, butless cutting ability. The lower duty cycle modes also increase the peakvoltage for the same power. Both the power and duty cycle may beadjusted together to keep the peak voltage consistent while reducing thecutting ability. If the peak voltage was not kept constant, then the arcdistance would increase as the duty cycle was reduced. The controller324 may initiate a cutting waveform having high power or a 100% dutycycle when tissue contact is sensed (i.e., resistive impedance issensed), and then switch to a lower power or a duty cycle less than 100%to increase drag after the initial cut is started.

FIG. 7 is a flow diagram of a method 700 of controlling electrosurgicalenergy delivered to the electrode of an electrosurgical instrument basedon sensed arcing patterns in accordance with embodiments of the presentdisclosure. After starting in step 701, electrosurgical energy isdelivered to the electrode of the electrosurgical instrument in step702. In step 704, arcing patterns of electric arcs formed between theelectrode and tissue are sensed. As described above, a arcing patternsmay be sensed in a variety of ways. In step 706, the level ofelectrosurgical energy delivered to the electrode is controlled based onthe sensed arcing patterns. Then, in step 707, the method ends.

FIG. 8 is a flow diagram of a method 800 of controlling electrosurgicalenergy to achieve a user-selected predetermined drag force based onsensed arcing patterns in accordance with embodiments of the presentdisclosure. After starting in step 801, a predetermined drag forcesetting is received from a user interface in step 802. In step 804,electrosurgical energy is delivered to an electrode of anelectrosurgical instrument. In step 806, arcing patterns between theelectrode and tissue are sensed. In step 808, a drag force is determinedbased on the sensed arcing patterns.

Next, in step 810, it is determined whether the determined drag force isless than the predetermined drag force setting. If so, the power of theelectrosurgical energy delivered to the electrode is decreased or,alternatively, the duty cycle of the output RF waveform is decreased instep 812 and the method 800 returns to step 806. If it is determinedthat the determined drag force is not less than the predetermined dragforce setting, it is determined whether the drag force is greater thanthe predetermined drag force setting, in step 814. If it is determinedthat drag force is greater than the predetermined drag force setting,then the power of the electrosurgical energy delivered to the electrodeis increased or, alternatively, the duty cycle of the output RF waveformis increased in step 816 and the method 800 returns to step 806. If itis not determined that drag force is greater than the predetermined dragforce setting, then the method 800 returns to step 806 to continuesensing arcing patterns between the electrode and tissue.

FIG. 9 is a flow diagram of a method 900 of detecting arcing patternsbased on impedance according to embodiments of the present disclosure.After starting in step 901, the voltage and current of theelectrosurgical energy is sensed 902, e.g., by the voltage and currentsensors 370, 380 of FIG. 3. In step 904, changes in impedance over timeis calculated, e.g., by the controller 324, based on the sensed voltageand current. Then, before ending at step 907, arcing patterns aredetected in step 906, e.g., by the controller 324, based on thecalculated changes in impedance over time.

FIG. 10 is a flow diagram of a method 1000 of controlling powerdelivered to an electrode of an electrosurgical instrument based on dragthat is determined from an analysis of the harmonic distortion of atleast one of sensed voltage and current waveforms according toembodiments of the present disclosure. After starting, in step 1001, atleast one of the voltage and current waveforms of the electrosurgicalenergy delivered to an electrode of an electrosurgical instrument issensed, in step 1002. In step 1004, at least one of the voltage andcurrent waveforms are filtered with respect to frequency to detectharmonic distortion. In step 1006, drag is determined based on thedetermined harmonic distortion.

Next, in step 1008, it is determined whether the determined drag is lessthan the predetermined drag setting, e.g., provided by a surgeon via auser interface. If so, the power level of the electrosurgical energydelivered to the electrode is increased in step 1010 and the method 1000returns to step 1002. Otherwise, in step 1012, it is determined whetherthe determined drag is greater than the predetermined drag setting. Ifit is determined that the determined drag is greater than thepredetermined drag setting, the power level of the electrosurgicalenergy delivered to the electrode is decreased in step 1014 and themethod 1000 returns to step 1002. If it is not determined that thedetermined drag is greater than the predetermined drag setting in step1012, then the method 1000 returns to step 1002.

FIG. 11 is a flow diagram of a method of controlling drag based onarcing patterns determined from sensed impedance between the electrodeof an electrosurgical instrument and tissue according to embodiments ofthe present disclosure. After starting in step 1101, impedance betweenthe electrode and tissue is sensed in step 1102. If, in step 1103, it isdetermined that the sensed impedance is a high capacitive impedance,then a loss of arcing is detected in step 1104. If, in step 1105, it isdetermined that the sensed impedance is a low inductive impedance, thenarcing is detected in step 1106. If, in step 1107, it is determined thatthe sensed impedance is a resistive impedance, as opposed to capacitiveor inductive, then contact with tissue is detected in step 1108. Contactwith tissue may first be detected when a low resistive impedance (e.g.,100-700 ohms for many types of tissues) is sensed. Then, in step 1109,the arcing pattern information obtained through steps 1102-1108 isanalyzed and a drag level is determined based on the arcing patterninformation.

Next, in step 1110, it is determined whether the determined drag is lessthan a predetermined drag setting. The predetermined drag setting may bepreset in the handset, it may be automatically determined based onsurgeon usage, or it may be set by the surgeon via a user interface onthe handset. If it is determined that the determined drag level is lessthan a predetermined drag setting, the power of the electrosurgicalenergy delivered to the electrode is decreased in step 1112 and themethod 1100 returns to step 1102. In other words, if the impedance ishigh, the electrode is not in contact with the tissue, thus creating alow drag condition. The power could be lowered or the voltage may beincreased to increase the distance by which arcs can be established,thus increasing coagulation. In addition, the RF waveform may be changedto keep the average power constant but with a high voltage (i.e., thefulguration mode). Otherwise, in step 1114, it is determined whether thedrag level is greater than the predetermined drag setting.

If it is determined that drag is greater than the predetermined dragsetting, then the power of the electrosurgical energy delivered to theelectrode is increased in step 1116 and the method 1100 returns to step1102. In other words, if the impedance is a resistive impedance, thenthe blade is in contact with the tissue, which is a high drag condition.Thus, the power is increased to vaporize more tissue. The RF waveformmay also be changed to a cut pattern to lower the voltage and increasecutting energy. If it is not determined that drag force is greater thanthe predetermined drag force setting, then the method 1100 returns tostep 1102 to sense arcing patterns between the electrode and tissue.

If the sensed impedance stays high without arcs for an extended period,then the user has likely pulled the electrosurgical instrument 2 fromthe tissue. In this case, the electrosurgical generator would enter alower-power state with just enough power for impedance sensing. Then,when the electrode makes contact with the tissue again, the controllerwould increase the power rapidly and then adjust for desired drag.

FIG. 12 is a flow diagram of a method 1200 of sensing arcing patternsbased on the phase difference between the sensed voltage and current ofthe electrosurgical energy according to embodiments of the presentdisclosure. After starting in step 1201, the voltage and current of theelectrosurgical energy is sensed 1202, e.g., by the voltage and currentsensors 370, 380 of FIG. 3. In step 1204, the phase difference betweenthe sensed voltage and current is calculated, e.g., by the controller324, based on the sensed voltage and current. Next, in step 1206, theaverage phase difference over a predetermined time interval iscalculated. Then, before ending at step 1209, arcing patterns areestimated in step 1208, e.g., by the controller 324, based on thecalculated average phase difference over a predetermined time interval.

It is understood that any or all of the steps of the methods orprocesses of FIGS. 7-12 described above may be implemented in software,hardware (e.g., an FPGA), or a combination of software and hardware. Insome embodiments, any or all of the steps of the methods or processes ofFIGS. 7-12 described above may be implemented as program instructionsstored in the memory 326 and executed by the processor 325 of thegenerator circuitry 300 shown in FIG. 3. In other embodiments, any orall of the steps of the methods or processes of FIGS. 7-12 that involveanalyzing and/or sensing voltage and/or current waveforms may beimplemented by an FPGA.

While the present invention has been particularly shown and describedwith reference to the preferred embodiments thereof, it will beunderstood by those skilled in the art that the foregoing and otherchanges in form and details may be made therein without departing fromthe spirit and scope of the invention. Therefore, the above descriptionshould not be construed as limiting, but merely as exemplifications ofpreferred embodiments. Those skilled in the art will envision othermodifications within the scope and spirit of the present disclosure.

For example, a method of controlling electrosurgical energy wouldinclude detecting an arc and halting the RF delivery to stop the arc, asin bipolar or ligasure modes, or to encourage the arc, as in coagulationmodes.

What is claimed is:
 1. A method of controlling electrosurgical energy provided by an electrode of an electrosurgical instrument to tissue: delivering electrosurgical energy to the electrode of the electrosurgical instrument; sensing arcing patterns between the electrode and tissue; and controlling the level of electrosurgical energy delivered to the electrode based on the sensed arcing patterns.
 2. The method according to claim 1, further comprising: determining drag based on the sensed arcing patterns; and controlling the level of electrosurgical energy delivered to the electrode based on the determined drag and a predetermined drag value.
 3. The method according to claim 2, further comprising receiving the predetermined drag value from a user interface.
 4. The method according to claim 2, further comprising reading the predetermined drag value from a bar code, an RFID tag, or a memory associated with the electrosurgical instrument.
 5. The method according to claim 2, wherein controlling the level of electrosurgical energy delivered to the electrode includes increasing the power delivered to the electrode if the determined drag is greater than the predetermined drag value and decreasing the power delivered to the electrode if the determined drag is less than the predetermined drag value.
 6. The method according to claim 2, wherein the electrosurgical energy delivered to the electrode is in the form of an RF waveform, and wherein controlling the level of energy delivered to the electrode includes adjusting the duty cycle of the RF waveform to change the drag.
 7. The method according to claim 1, wherein sensing the arcing patterns includes: sensing at least one of the voltage and current waveforms of the electrosurgical energy delivered to the electrode; and detecting harmonic distortion of the at least one of the voltage and current waveforms.
 8. The method according to claim 7, wherein detecting harmonic distortion includes filtering with respect to frequency the at least one of the voltage and current waveforms.
 9. The method according to claim 7, wherein detecting harmonic distortion includes applying a Fast Fourier Transform (FFT), a Discrete Fourier Transform (DFT), a Goertzel filter, or a narrow-band filter to the at least one of the voltage and current waveforms.
 10. The method according to claim 7, wherein detecting harmonic distortion of the at least one of the voltage and current waveforms includes detecting at least one of the second, third, and fifth harmonics of the at least one of the voltage and current waveforms.
 11. The method according to claim 1, wherein sensing arcing patterns includes: sensing the voltage and current waveforms of the electrosurgical energy delivered to the electrode; and calculating the normalized difference between the voltage and current waveforms.
 12. The method according to claim 1, wherein sensing arcing patterns includes: sensing the voltage and current of the electrosurgical energy; calculating impedance based on the sensed voltage and current; and detecting the arcing patterns based on the change in calculated impedance over time.
 13. The method according to claim 1, wherein sensing arcing patterns includes: sensing the voltage and current of the electrosurgical energy; calculating the phase difference between the sensed voltage and current; calculating the average phase difference over a predetermined time interval; and sensing the arcing patterns based on the average phase difference.
 14. The method according to claim 1, wherein sensing arcing patterns includes: sensing impedance between the electrode and tissue; detecting arcing if a low inductive impedance is sensed; detecting a loss of arcing if a high capacitive impedance is sensed; and detecting contact with tissue if a resistive impedance is sensed.
 15. The method according to claim 14, further comprising: determining drag based on the sensed arcing patterns; and controlling the level of electrosurgical energy delivered to the electrode based on the determined drag and a predetermined drag value.
 16. An electrosurgical generator for providing electrosurgical energy to an electrode of an electrosurgical instrument, the electrosurgical generator comprising: an output stage configured to provide electrosurgical energy to the electrode of the electrosurgical instrument; a sensor configured to sense arcing patterns of the electrosurgical energy provided to tissue by the electrode; and a controller coupled to the output stage and the sensor, the controller configured to control the level of electrosurgical energy delivered to the electrode based on the sensed arcing patterns.
 17. The electrosurgical generator according to claim 16, wherein the controller is further configured to determine a drag force on the electrode of the electrosurgical instrument based on the sensed arcing patterns and to control the level of electrosurgical energy delivered to the electrode based on the determined drag force and a drag force setting.
 18. The electrosurgical generator according to claim 17, further comprising a user interface configured to provide the drag force setting to the controller in response to a user selection.
 19. The electrosurgical generator according to claim 17, wherein the controller is configured to control the level of electrosurgical energy delivered to the electrode by increasing the power delivered to the electrode if the determined drag is greater than the drag force setting and by decreasing the power delivered to the electrode if the determined drag is less than the drag force setting.
 20. The electrosurgical generator according to claim 16, wherein the sensor includes at least one of a voltage sensor and a current sensor, and wherein the controller is configured to detect harmonic distortion of at least one of the voltage and current waveforms output from the at least one of the voltage and current sensors, respectively. 